1. Field of the Invention
The present invention relates to pick and place machines used in the assembly of components on substrates and printed circuit boards, etc. More particularly, the present invention relates to a new method for placing an eye point or feature of a semiconductor die in a precise registration with a target eye point on the substrate or carrier or printed circuit board.
2. Description of the Prior Art
The present invention involves the use of known prior art pick and place machines which are manufactured and sold by over twenty major manufacturers worldwide. Heretofore, components such as semiconductor chips, resisters, capacitors, inductors, etc. are picked from the pockets of tape feeders or waffle packs, etc. and were placed on a precise target location on a substrate or PC board. The component to be placed cannot be picked up in perfect orientation for placement, thus, it is necessary to use some form of vision system after picking up the component and before placement to assure proper placement registration.
Modern pick and place machines are provided with pick up heads having a vacuum nozzle movable in the vertical or Z direction. The head or heads are mounted on an X-Y gantry which permits any component picked from a supply location to be transferred to a target or placement location and placed on a substrate or PC board. The problem of highly accurate positioning can be resolved by transporting the picked component over a look-up vision system having a known physical displacement from the placement location. The actual position of the pattern on the bottom of the die or the edges of the die can easily be determined by the vision system. Corrections are made for X-Y and theta (xcex8) pick-up errors and the placement of the components can be made to the accuracy permitted by the gantry drives and encoder in the pick and place machines. Such vision systems are supplied to manufacturers of pick and place machines by Cognex, ICOS, and AISI and others.
In order to assure more accurate pick-up of components, manufacturers of pick and place machines have placed look down vision systems on the pick-up head which determine the size, type and orientation of a component prior to picking up the component with a vacuum nozzle. Such systems are needed when components are placed in waffle trays where the component can move and lose their original orientation.
As an alternative, on the head horizontal imaging systems such as that shown and described in U.S. Pat. No. 5,559,727 may be used in place of a look up vision system. Since the horizontal vision system operates on the fly, substantial time savings can be made.
All of the types of vision systems can be incorporated into most pick and place machines which are employed to place components on substrates. It has been suggested that these machines be modified to solve a problem that has arisen with the manufacture of fiber optic connectors or interfaces. It is recognized that the look up vision system can be used to accurately place the bottom features or edges of a component on a target position on a substrate. However, if a fiber optic diode detector is on the upper surface of the die, the look up system only places the features with the accuracy of which the feature is positioned to the edges of the die. Since most die are saw cut from a wafer, the edges of the die outside the surface pattern may vary a few one-thousandths of an inch. If a plurality of diode drivers or sensor chips are placed on a substrate connecter with an error introduced by the variable width of the street material outside of the circuit pattern, there may be an accumulated error difference between different die on the same substrate.
Accordingly, a simple method of eliminating deviation errors between different die when the distance varies from the edge of the die to an active feature is needed.
It is a principal object of the present invention to provide a novel method of placing die or components having active surface features so that the feature and not the predetermined edges of the die are placed on a target position.
It is a principal object of the present invention to provide a method of locating features on top of a die onto substrates so that the feature and not the edges of the die are located relative to each other as accurately as the pick and place machine can locate die on a placement target.
It is a principal object of the present invention to provide a substrate populated with a plurality of die so that the active features on the different die are located relative to each other as accurately as the pick and place machine is capable of placing components.
It is a general object of the present invention to provide a substrate populated with plural light sensitive detectors or emitters located apart from each other on a known or standard spacing or pitch with a minimum of deviation error.
It is a general object of the present invention to provide a prior art look down camera on the head of a pick and place machine to determine the position of a die before pick up and using the standard look down vision system to determine a center target and orientation of the die prior to picking up with a vacuum nozzle. Further, with the information acquired by the look down camera the position of the active feature to be placed relative to the perimeter edges can be determined so that the eye point of the active feature and not the edges of the component may be placed on the desired X-Y target.
It is a general object of the present invention to provide a substrate for a connector on which a plurality of active features or components or die are mounted precisely spaced one from another using existing pick and place machines.
It is a general object of the present invention to provide a known pick and place machine with a pick preview vision camera system and a horizontal imaging system programmed to place surface features on the die at a predetermined X and Y target position on a substrate.
It is a general object of the present invention to provide a method that may be used in known commercially available pick and place machines that eliminates the need a look up vision system and enables continuous on the fly placement of components having active top surface features.
According to these and other objects of the present invention there is provided a pick and place machine with a pick preview vision system on the pick up head for obtaining an X-Y location of a feature on the die. The system determines the centroid of the feature on the die to be placed. Having a horizontal on the fly vision system on the same pick up head,the system determines the centroid of the same die in space relative to the vision system, thus permits the control system to determine the offset error for accurate placement of the surface feature on the die on the predetermined X-Y position of the substrate.